1. Field of the Invention
The present invention relates generally to switches, and, more particularly, to a trolley wire insulator switch for use in underground mine haulage systems.
2. Description of the Prior Art
In underground mining operations, upon entry into the mine, long distances must frequently be traversed before reaching the mining area. In order to expedite transportation of personnel and equipment to and from the mining area, rail mounted vehicles are frequently employed.
Electrically operated mine vehicles which run on rails extending into the mine are typically powered by overhead trolley wires, through trolleys attached to the vehicles. The trolley moves along the trolley wire as the vehicle moves along the track thereby providing the electrically operated mine vehicle with a continuous supply of power. The power system is typically a DC system in which the trolley wires are biased with a positive potential, and the rails upon which the vehicles are mounted complete the DC circuit by acting as the ground connection.
The vehicles must be capable of transporting weights of several tons, and, therefore, must utilize heavy duty DC motors. Problems develop in such electrically-operated systems as the vehicles travel into the mine away from the DC power source since the current available for operation of the DC motor diminishes due to resistive losses of the trolley wire. To overcome this problem, in most mine haulage systems, high current capacity feeder cables are directly connected to the DC power source instead of the trolley wire. The feeder cables run in directions parallel to those of the trolley wires, but are of a greater diameter to provide the higher current capacity thereby. The trolley wires must be of a diameter to allow connection to the vehicle trolley, precluding any increase in the diameter of the trolley wire, thus limiting any increase in the current capacity of the trolley wire as the power requirements of the mining operation increases. By coupling the feeder cable to the trolley wire at periodic intervals, the current level required to operate the heavy duty DC motors may be maintained along the entire length of the trolley wire.
In such systems, the feeder cables are coupled to the trolley wires through section insulator switches. Such switches serve to couple both the feeder cable to a section of trolley wire and also to connect successive sections of trolley wires and feeder cables. The switches allow manual openings thereof in order to disconnect the system downstream of the switch when not needed, such disconnection being desired for safety reasons.
A modular section insulator switch is disclosed in U.S. Pat. No. 4,365,129. The switch described therein allows connection of feeder cables of different diameters thereto. Reuse of such a switch is therefore allowed when larger diameter feeder cables are installed in a mine haulage system to increase the current carrying capacity thereby as mining operations expand in the mine.
Also known in the art are provisions to include fuses in the section insulator switches as a safety measure in the event of a fault along a section of trolley wire. In existing switches containing such fuses, however, the fuse is located in the body of the switch in close proximity to the high current feeder cables. Replacement of a fuse from such a location is therefore a potentially hazardous task.
Accordingly, it is the object of the present invention to provide a fusible-trolley-insulation switch in which the fuse is located such that it may be quickly and safely replaced after the occurrence of a ground fault.